With the development of various types of broadband services, customers have increasing requirements for rates, a current long-term requirement for a user broadband rate in the industry may reach 400 Mb/s, and a broadband using the traditional digital subscriber line (DSL) technology has no competitive edge. The Fiber to the Home (FTTH) technology, represented by a passive optical network, has been able to meet the bandwidth requirement, but problems that are difficult to resolve exist in many aspects such as investment costs, laying and operation and maintenance, and stability, and copper access technologies such as DSL have obvious relative advantages in aspects such as investment costs and operation and maintenance.
Carriers wish to provide broadband access services that meet user requirements in a relatively long time in the future while existing copper wire resource investments are protected and used. Such copper wire technology expected by the carriers are mainly oriented to a scenario in which a length of a remaining copper wire is approximately 200 m, may provide a total rate of up to 500 M, and also features low complexity, low power consumption, and easy operation and maintenance. With deepening of construction of various types of Fiber to the x (FTTx), a distance between a fiber and a user is becoming increasingly short, a length of a remaining copper wire connecting a fiber to a user equipment is even less than 200 m, and the Orthogonal Frequency Division Multiplexing (OFDM) technology that meets the requirement for a higher rate, reduces transmission distances, and spreads the spectrum is an inevitable choice based on a current copper wire technology.
An OFDM system that uses the Overlapped Spectrum Duplex (OSD) technology to transmit and receive signals is called an OSD-OFDM system. The system replaces generally used frequency division duplex or time division duplex, enabling the uplink and downlink signals to completely multiplex channels on all frequency bands at the same time, and spectral efficiency is expected to be doubled.
In the OSD-OFDM system in the prior art, a power spectral density (PSD) of transmitted signals between a headend and a peer end is generally a value used according to a specification. In an actual application, however, different scenarios have different channel attenuation, and transmitting uplink and downlink signals on all frequency bands or retaining a same power spectral density for transmitting signals may lead to a relatively large echo signals that are looped back in a hybrid loopback manner to a receiver of a local end, which increases interference of transmitted signals in received signals and deteriorates system performance.